The overall objectives of the project are to determine how radiation and radiomimetic agents affect living organisms and how, in turn, the organisms respond to these effects. Specifically, we shall carry out investigations with 1on strains which have the property of filamenting subsequent to exposure to ultraviolet irradiation or radiomimetic chemicals. We have shown that it is possible to induce filaments in 1on strains by irradiating replicons prior to their transfer into Fminus strains. Furthermore, the integration of F into the bacterial genome of 1on strains has been shown to result in a condition of spontaneous filamentation. We intend to further investigate the nature of this recombinational event. In addition, we intend to examine the effect of 1on and sul upon the regulation of enzymes functional in polysaccharide synthesis in an attempt to determine the nature of the 1on plus product. Strains with the exrB mutation also filament spontaneously. We have mapped the position of exrB to be near that of exrA and uvrA. We propose to make a complete analysis of the properties of this mutation in relationship with other genes associated with UV resistance.